Sunday, September 13, 2020

Chapter 8: Induction Motor-Page 2

  Chapter 8: Induction Motor-

11. In some induction motors, copper bars are placed deep in the rotor. It is done so that
A. slip under normal running conditions is reduced
B. p.f. is improve
C. starting torque is increased
D. output is increased


... Answer is (C)

 

 
 

12. The fractional slip of an induction motor is the ratio
A. rotor Cu loss/rotor input
B. stator Cu loss/stator input
C. rotor Cu loss/rotor output
D. rotor Cu loss/stator Cu loss

... Answer is (A)

 
 
 

13. Which method is the least used for 3-phase motor starting?
A. Y-Δ
B. auto-transformer
C. across-the-line
D. primary resistors

... Answer is (A)

 

 
 

14. In case of the induction motors the torque is
A. inversely proportional to (slip)²
B. directly proportional to (slip)²
C. inversely proportional to slip
D. directly proportional to slip

  ... Answer is (D)

 

 
 
15. The torque developed in the cage induction motor with autostarter is
A. K/torque with direct switching
B. K x torque with direct switching
C. K2 x torque with direct switching
D. K2/torque with direct switching
  ...
Answer is (C)

 
 
 

16. For which motor the speed can be controlled from rotor side?
A. Squirrel-cage induction motor
B. Slip-ring induction motor
C. Both (a) and (b)
D. None of the above

  ... Answer is (B)

 

 
 

17. If any two phases for an induction motor are interchanged
A. the motor will run in reverse direction
B. the motor will run at reduced speed
C. the motor will not run
D. the motor will burn

... Answer is (A)

 
 

18. An induction motor is
A. self-starting with zero torque
B. self-starting with high torque
C. self-starting with low torque
D. non-self starting

... Answer is (C)

 
 

19. The maximum torque in an induction motor depends on
A. frequency
B. rotor inductive reactance
C. square of supply voltage
D. all of the above

 
  ... Answer is (D)

 
 

20.  In three-phase squirrel-cage induction motors
A. rotor conductor ends are shortcircuited through slip rings
B. rotor conductors are short-circuited through end rings
C. rotor conductors are kept open
D. rotor conductors are connected to insulation

  ... Answer is (B)

 

 

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